Supervision and monitoring of a system, in the following exemplified by a power network, is of great importance for ensuring proper functioning of the power network and for enabling right action to be taken. It is important that the operator of such the power network is enabled to quickly understand the status of the network and in particular to detect any fault conditions and to act rapidly upon such fault conditions.
The operator is supported in his or her task by a supervisory control system, which in the art is also known under the term SCADA (Supervisory Control and Data Acquisition) system. Such a supervisory control system interacts with the power network via system interface units. The units may for example obtain measurements from the power network and perform control actions on the power network. A supervisory control system comprises processing means to process the information coming from and going to the system interface units, data storing means to store measurements as well as data generated from the processing of measurements, such as alarms, statistical calculations etc., a human-machine interface in the form of at least one operator terminal and communication means for signal transmission from and to the system interface units and for data transmission between the processing means, the data storing means and the human-machine interface. The operator terminal comprises one or several display units showing different parts and data of the power network. It is inevitable that for large power networks, a huge amount of data is available to be displayed and needs to be monitored by an operator. The visual information or data should be presented to the operator in the best way possible, offering a best possible overview.
One type of information that is of importance to the operator of the power network is the actual power flow on the power transmission or distribution lines of the power network. The power flow can thereby be divided into active or real power flow, measured in VA (Volta-Ampere), and reactive power flow, measured in VAR (Volt-Ampere-Reactive).
Intuitive visualization of the flow of real and reactive power has proven to be difficult. Presently, only very simple visualization methods, usually comprising the use of arrows of different shapes, are available as a support for the operator of the power network. In FIG. 1, one such approach for displaying power flow is shown, known from a report which is downloadable from the Internet: Thomas. J. Overbye et al., Effective Power System Control Center Visualization. Power Systems Engineering Research Center; Final Report, PSERC Document 08-12, May 2008. Animated arrows 40 demonstrate the transmission flow of real power. The animated arrows move along the displayed power lines and the size of the arrows indicates the amount of transmission flow. These arrows 40 can be visually disturbing to the operator for example when they are presented in an overview picture of the power network covering hundreds of power lines. The arrows may clutter the overview picture and details may be difficult to see underneath the large arrows. If they are further combined with arrows showing the transmission flow of reactive power at the same time, the visual representation would cover an animation of two kinds of arrows that move in opposite directions, the arrows having different sizes. The overwhelming or even irritating effect of such a graphical representation is easily imaginable.
Such methods scale up poorly in visual terms and the operator gets lost in details when hundreds of animated arrows start to draw the operator's attention to each individual power line. In addition, the arrowheads cause severe clutter on the display.